1. Field of the Invention
The present invention relates to a swivelling working vehicle which comprises a swivel base equipped with a working device, a hydraulic motor causing the swivel base to rotate, and an actuator valve adapted to drive the hydraulic motor in forward and reverse directions or to stop said motor. More particularly, the invention relates to a swivelling working vehicle which besides the above members further comprises a setting adjustor for predetermining rest or stoppage positions of the swivel base, flow control valve means for controlling flow rate of oil delivered to the hydraulic motor and an electric control circuit which automatically controls the actuator valve and the control valve means on the basis of signals generated by and delivered from a sensor and a detector, the sensor adapted to measure an angular position of the swivel base with respect to the vehicle body while the detector being adapted to sense a shifted state of the actuator valve. In other words, the invention relates to a working vehicle having a structure such that a control of swivelling motion of the swivel base is simplified so as to improve a working efficiency of the vehicle comprising a swivel base operated by means of a hydraulic motor.
2. Description of the Prior Art
It is already known to provide a swivelling working vehicle with a control device which is designed merely to automatically stop a swivel base by means of an actuator valve and flow control valve means in such a manner that said swivel base is caused to stop smoothly without any violent shock.
The known vehicle is however disadvantageous in that the swivel base is abruptly accelerated to start its swiveling motion. Such a violent start of said motion brings about many problems such as dropping down of loaded material and a change in attitude or position of the vehicle body due to a reaction caused by the abrupt start. This makes it uncomfortable for an operator to drive the vehicle. Moreover, the swivelling speed varies remarkably when said vehicle is located on a slope where an inertia of swivelling members will be undesirably increased or decreased. Consequently, the swivel base cannot be stopped exactly at a predetermined angle, thus resulting in a lowering of working efficiency. It has therefore been desired to improve the automatic control of the swivel base.